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I thought of something like this when I was planning my buck (mould) but as DD says my concern would be leaving impressions in the form which would be difficult if not impossible to remove. I'm going to drill the row of small holes along the perimeter of mine & try it out using a thinner material than DD has used. I'm thinking 3mm Polycarbonate. It should stretch to leave 1mm thickness at the thinnest areas, it'll be strong (used on RC buggy body's) & hopefully flexible enough to go over the undercuts for removal. I expect it'll still put up a bit of a fight though

DD have you tried a thinner material?

For the first alien, they made the first printed with a departure of 3 mm sheet. I did not like, because in the upper part (where the material becomes thinner), was too soft (question of taste). But the extraction remained a problem. But I never tried to cut the piece, leaving the mold. If you build the machine vacuum, you can do all the tests you want, for both thicknesses, and for cutting. I still doubt if you can not damage the mold along the cutting line. You have to try and take risks.

Thanks friends,
I have tried in making silicone molds, jacketed fiberglass. The product material is a resin which hardens in 6 minutes and has mechanical characteristics similar to ABS. I cast only once. The surface is very smooth, as the model, but the last millimeter the tips of some teeth have failed, because of a small bubble of air. An expert explained to me that must be achieved this tips with a small brush, during casting, to allow the resin to reach those areas.

.

As the teeth of the monster are chrome, I must try a resin with aluminum powder, rather than paint with chrome paint, which is more problematic. This new resin after it has been polished, could shine as a chromed metal. Someone has already tried?

Right, To reduce the chance of getting bubbles in the tips of the teeth you can try cutting the silicone mould part like this:

Use a scalpel & cut right through the silicone from the tips of the teeth. Then before you cast, use talcum powder & dust the inside of the mould thoroughly with a soft brush! including the cuts you've made! Then blow out any excess powder.
This will help to draw your casting resin into the cuts preventing the bubbles from forming. You may have a little flashing between the teeth but its easy to remove & preferable to bubbles.
Its worked for me

For the chrome don't give up on paint just yet Have you tried Alclad chrome?

I never tried Alclad Chrome. I saw some videos of this paint. A few days ago I ordered the resin metal to try it. If the result does not satisfy me, I'll try the paint Alclad, because it looks great. I wanted to try the resin, because I imagine that it can not lose the shine, after bringing the metal surface by polishing. While I fear that the paint is more delicate. It could fall out when ALIEN chew bones. Maybe the liquid metal does not become mirror how the paint.

Man,..this all looks wonderfull.
If i came this far with the bust i would pour the teeth in white metal.
Some siliconerubbers can handle quite some heat, so after some good resin pours i would give it a try with the white metal.

Use a scalpel & cut right through the silicone from the tips of the teeth. Then before you cast, use talcum powder & dust the inside of the mould thoroughly with a soft brush! including the cuts you've made! Then blow out any excess powder.
This will help to draw your casting resin into the cuts preventing the bubbles from forming. You may have a little flashing between the teeth but its easy to remove & preferable to bubbles.
Its worked for me

HTH

Leigh said:

For the chrome don't give up on paint just yet Have you tried Alclad chrome?

The problem of air bubbles on the tips has been resolved with brush during casting.

This is the result of a few minutes of rubbing with steel wool, done only on the visible part of the teeth. The resin was still slightly sticky. Maybe have to wait a few days to have a surface that sticks less, to get a better mirror effect. However in the data sheet it says that you can polish with the creams for the body, to get the maximum and then protect with varnish. I do not care a chrome exceptional, because it seems to me that the original was more similar to that obtained with steel wool. But the chrome plating adorns and I believe that the manufacturing steps of the painted version, in addition to returning chrome exceptional, are also less labor intensive. A contraindication of this resin is the weight. With the plastic of the molds preceding the teeth weigh 36.6g, while these weigh 90g, that is, the weight multiplied by 2.5.

That's Perfect!
I might have to steal that idea off of you... if you don't mind that is

I've already taken many ideas from you. I also own a dremel and maybe I could increase the mirror. Being a metal, it can oxidize. In the data sheet advise to protect with varnish. I have to try what happens with transparent, if it keeps the mirror surface.

This is the groin. It's my first piece printed with polyurethane. The density appears to be 130kg / m3,instead of 90 free-foam. I got it in two shots,adding foam to the same piece, because the first was not completely filled. This first printed I needed to find the true density.

Thanks Leigh.
It is interchangeable with a car interior part (the flux) of back to the future.

The final print will be even better, because it will be done in one fell swoop and with greater density. In some molds also inject the liquid plastic, to obtain the surface. For other parts I will stretch the plastic, with brush. It is a more robust than plastic polyurethane casting. It is one that is used in flooring. I also have to think about how to get a skin-like surface roughness, alien of course.

Yes, all my molds are glass fiber and gelcoat. For reasons of cost, only the molds of the details, such as fingers, head bulbs, pumps, teeth and spurs are made of silicone rubber and fiberglass.

All parties were created as possible without undercuts, trying not to alter the appearance of the original subject. Where it was not possible to follow physiognomy, then I take away with milling or rasp, but they are small areas. In others, I used the blocks, created with gelcoat injections.

The mandible is the last mold to build. I'm still undecided whether to also use silicone. Probably I'm going to see how you did.

This is the right arm. For safety, I made the density of 150kg / m3. It came very well and very hard. I was afraid that it would be difficult to remove the mold. Instead it comes off immediately without even a gram of effort. With the wax does not even stick a little.